1. Field
The disclosed and claimed concept relates generally to control circuitry and, more particularly, to an improved apparatus for detecting a position of a rod such as a drive rod that is movable within a passageway such as an interior of a drive rod housing within a nuclear containment.
2. Related Art
Nuclear power plants are generally well known and can be said to include nuclear reactors that may typically be a Pressurized Water Reactors (PWRs) or Boiling Water Reactors (BWRs). Nuclear power plants having a PWR can generally be stated as comprising a reactor that includes one or more fuel cells, a primary loop that cools the reactor, and a secondary loop that drives a steam turbine which operates an electrical generator. Such nuclear power plants typically additionally include a heat exchanger between the primary and secondary loops. The heat exchanger typically is in the form of a steam generator which comprises tubes that carry the primary coolant and a plenum that carries the secondary coolant in heat-exchange relationship with the tubes and thus with the primary coolant. Alternatively, a BWR power plant typically operates at relatively lower pressures and temperatures and employs fuel cells that generate steam which is provided directly to a steam turbine.
The nuclear reaction that occurs within a fuel cell typically is controlled by a number of control rods that are translatable into and out of the fuel cells in a known fashion. The control rods typically are operated by drive rods that are connected directly with the control rods and that are moveably situated within drive rod housings disposed above the fuel cells. Since the control rods control the reaction of the fuel cell, it is desirable to know the precise position of each control rod at all times.
Previous systems for determining the positions of control rods have relied upon a plurality of detectors mounted outside and concentric with a drive rod housing, with the detectors each consisting of a coiled wire slipped over the housing and spaced along its length at regular intervals such as 3.75 inch intervals. As the drive rod moves past the coils, the magnetic flux from the coils changes, and the changing magnetic flux would be processed by signal processing systems.
While such systems have been generally effective for their intended purpose, they have not been without limitation. The various coils have required cable assemblies and AC current to generate the needed electromagnetic field. Also, the accuracy of a detector having coils spaced as mentioned above is only within a range of 3.125 inches. It thus would be desirable to provide a simpler system that provides better accuracy.